The present invention relates to a hybrid deposition system. The invention further relates to a deposition system, which combines features of metal-organic chemical vapor deposition with hydride vapor-phase epitaxy. The present invention also relates to a method of forming semiconductor heterostructures, by two different deposition techniques, in a single reactor.
Hydride vapor-phase epitaxy (HVPE) is an important technique for the epitaxial growth of various semiconductors, such as gallium nitride. Gallium nitride (GaN) is emerging as an important technological material.
For example, GaN is currently used in the manufacture of blue light emitting diodes, semiconductor lasers, and other opto-electronic devices. The background of the related art will be discussed with particular reference to the deposition of GaN.
HVPE is a currently favored technique for GaN deposition, because it provides relatively rapid growth in a cost-effective manner. In this technique, growth of GaN proceeds due to the high temperature, vapor-phase reaction between gallium chloride (GaCl) and ammonia (NH3). The ammonia is supplied from a standard gas source, while the GaCl is produced by passing HCl over a heated liquid gallium supply. The two gases (ammonia and GaCl) are directed towards a heated substrate where they react to produce solid GaN on the substrate surface.
While HVPE allows for high growth rates of GaN, there are certain difficulties associated with HVPE as a technique for growing other III-V nitrides or GaN alloys. For example, it is difficult to grow materials such as aluminum nitride (AlN) or alloys of AlN and GaN (AlGaN) by HVPE. The problem lies in providing an adequate supply of aluminum chloride. The latter substance is extremely stable, and tends to form a solid with low vapor pressure even at the elevated temperature of a HVPE reactor. Thus, when HCl is passed over Al metal, the aluminum chloride that is formed tends to solidify and not to be carried towards the substrate.
A technique for growing both AlN and GaN layers on the same sample is desirable for several applications. For example, a buffer layer of AlN or AlGaN grown between an epitaxial GaN layer and a typical substrate such as sapphire (Al2O3) improves the quality of the GaN epitaxial layer. This improved quality results from closer matching of lattice constant and thermal expansion coefficient between the buffer layer and the GaN. In addition, it is often desirable to form heterostructures in which layers of AlN, GaN, and AlGaN, are grown on top of one another. Heterostructures find many applications in semiconductor lasers, light-emitting diodes (LED""s), high-electron mobility transistors, and other electronic and opto-electronic devices.
Similarly, it is also desirable to grow heterostructures including indium nitride (InN) and associated alloys (InGaN, InAlN, InAlGaN), in the same system. The use of InN increases the range of heterostructures that can be grown, leading to many new device applications. However, growth of InN by HVPE may present problems. For example, thin consistent layers of InGaN are difficult to fabricate using the high growth rates typically associated with HVPE techniques. Furthermore, for most device applications, it is necessary to selectively incorporate dopants to provide conductive materials. Junctions of material incorporating different dopant types are key elements of almost all electronic devices, such as the diode, the transistor, and the semiconductor laser. However, some dopant materials are best utilized in organo-metallic form.
A further drawback to HVPE of prior art methods and systems is that certain substrates cannot be incorporated into an HVPE system until a certain amount of epitaxial material has been grown. For example, it may be desired to grow GaN or related materials on silicon (Si) substrates. Alternatively, it may be desired to use compound substrates (consisting of more than one type of material), or patterned substrates. If any of these substrates are subjected directly to HVPE growth, they may be destroyed. This is due to the presence in HVPE reactors of certain gases, such as HCl, which act as etchants on HVPE-sensitive substrates (e.g., Si). It would be advantageous to provide a system and method for growth of a protective layer of epitaxial material by a method such as metal-organic chemical vapor deposition (MOCVD) before beginning HVPE growth, in which both deposition techniques (MOCVD and HVPE) are performed in the same reactor.
The present invention provides hybrid deposition systems and methods that overcome many of the above-described problems inherent in prior art deposition of GaN and related materials.
In view of the above, it is an object of the present invention to provide a hybrid deposition system for the efficient growth of aluminum nitride, indium nitride, gallium nitride, metal alloy-nitrides and related materials. Methods of the invention allow the incorporation of complex dopants and complex dopant mixtures into epitaxial layers and provides for the production of a large variation of film thicknesses and growth rates. Furthermore, methods of the invention can accommodate many different substrate types. According to one embodiment, the invention combines features of metal-organic chemical vapor deposition (MOCVD) and HVPE into a single, highly versatile, hybrid deposition system.
In the MOCVD growth technique of the prior art, ammonia gas is reacted with a metallo-organic compound at high temperatures above or on the substrate, leading to deposition of a solid semiconductor material. The present invention uses metal-organic sources and a HVPE reagent delivery chamber (e.g., liquid gallium supply), in a hybrid reactor. The system of the invention can be switched between operation in MOCVD mode and-HVPE mode, or can be operated in combined MOCVD/HVPE mode. Such switching between modes is easily achieved by changing the nature of the source or reagent gases supplied to the reactor, and by any appropriate changes to the operating or growth temperature of the reactor.
Briefly, to operate the hybrid system of the invention in MOCVD mode, at least one metallo-organic and ammonia gas are supplied to the reactor. To switch the hybrid system to HVPE mode, the metallo-organic supply is shut off, and a supply of a second reagent gas (e.g., GaCl) is provided by passing HCl over liquid metal (Ga). Generally, but not invariably, the temperature of the reactor may be changed when switching between HVPE mode and MOCVD mode.
Because both growth methods (MOCVD and HVPE) are incorporated into a single reactor system, it is possible to switch between the two techniques without interrupting deposition on the substrate or removing the sample from the reactor. This feature also increases the efficiency and decreases the cost of the method of the invention. According to systems and methods of the invention, AlN and thin InN layers can be conveniently grown (by MOCVD) in the same reactor as is used for the growth of thick GaN (by HVPE). Similarly, AlN, InN, GaN, and their alloys can be grown in the same reactor by, MOCVD and HVPE, either consecutively or concurrently. Therefore, a diverse array of heterostructures of AlN, InN, GaN and their alloys can be grown quickly and inexpensively using systems and, methods of the invention.
According to one aspect of the invention, a method is provided for growing III-V nitride layers on a non-native substrate, using both HVPE and MOCVD growth techniques simultaneously. As an example of this situation, two different source gases, such as GaCl and an aluminum-containing metallo-organic, are both supplied to the system together with ammonia. In this example, each source gas reacts with the ammonia gas at the location of the substrate, leading to deposition of AlGaN. InGaN or InAlGaN may be grown by an analogous method by supplying the appropriate source gases. Furthermore, dopants may be incorporated in layers of GaN or its alloys grown using the hybrid deposition system of the invention.
According to another aspect of the invention, a method is provided for using HVPE-sensitive substrates for deposition of III-V compounds by HVPE. Substrates that would normally be destroyed by HVPE growth, such as Si substrates or patterned substrates, are stable under MOCVD growth. A first, protective layer of a III-V compound is first grown on the substrate by MOCVD in the hybrid reactor. The hybrid reactor may then be switched to operate in HVPE mode, and at least one additional layer is formed by HVPE on the first layer. HVPE has the advantage of having a faster growth rate and is less expensive than MOCVD.
One feature of the invention is that it provides a hybrid deposition system. Another feature of the invention is that it provides a deposition system that can be operated in two different modes. Another feature of the invention is that it provides a hybrid MOCVD/HVPE deposition system. Another feature of the invention is that it provides a deposition system including a reactor and a plurality of heating units for heating the reactor.
One advantage of the invention is that it provides a hybrid deposition system which can be switched between MOCVD mode and HVPE mode and thus reducing the potential of introducing contamination of the structures produced that occur when switching from one reactor to another. Another advantage of the invention is that it provides a method for forming first and second III-V nitride layers, in which the first layer is formed by MOCVD in a hybrid reactor, and the second layer is formed by HVPE in the same hybrid reactor. Another advantage of the invention is that it provides a method of forming a III-V nitride layer by simultaneous deposition by MOCVD and HVPE. Another advantage of the invention is that it provides a hybrid deposition system including a reactor that is moveable with respect to at least one heating unit.
Yet another advantage of the current invention is that a high quality device structure can be produced by first producing a thin buffer layer by MOCVD, a thicker GaN layer by HVPE on the thin buffer layer and a third nitride layer on the thicker GaN layer by MOCVD.
These and other objects, advantages and features are accomplished by the provision of a hybrid deposition system, including: a reactor; a reagent delivery chamber having a reagent delivery chamber inlet, the reagent delivery chamber coupled to the reactor; at least one heating unit for supplying heat to the reactor; and at least one metallo-organic source coupled to,the reactor.
These and other objects, advantages and features are accomplished by the provision of a method of forming a semiconductor layer, including the steps of: a) arranging a substrate within a reactor; b) heating the reactor to a first growth temperature; c) supplying a first reagent gas and an organo-metallic vapor to the reactor to provide, by MOCVD, a first III-V nitride layer on the substrate; d) after step c), stopping the supply of organo-metallic vapor to the reactor; and e) while continuing to supply the first reagent gas to the reactor, supplying a second reagent gas to the reactor to provide at least one additional III-V nitride layer on the first III-V nitride layer.
These and other objects, advantages and features are accomplished by the provision of a method of forming a semiconductor layer, comprising the steps of: a) arranging a substrate within a reactor; b) heating the reactor to a first growth temperature; c) supplying a first reagent gas to the reactor; d) supplying a metallo-organic vapor to the reactor to provide, by MOCVD, a first III-V nitride layer on the substrate; e) after step d), while continuing to supply the first reagent gas and the metallo-organic vapor to the reactor, supplying a second reagent gas to the reactor to provide at least one additional III-V nitride layer on the first III-V nitride layer.
These and other objects, advantages and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following, or may be learned from practice of the invention. The advantages of the invention may be realized and attained as particularly pointed out in the appended claims.